A vacuum-tube, rackmount, adjustable power supply capable of +/- 1500
volts DC, 0 to 100mA output, with current limiting capability.

A power supply is a device that supplies electricalenergy to one or more electric loads.
The term is most commonly applied to devices that convert one form of
electrical energy to another, though it may also refer to devices that
convert another form of energy (e.g., mechanical, chemical, solar) to
electrical energy. A regulated power supply
is one that controls the output voltage or current to a specific value;
the controlled value is held nearly constant despite variations in
either load current or the voltage supplied by the power supply's energy
source.
Every power supply must obtain the energy it supplies to its load, as
well as any energy it consumes while performing that task, from an
energy source. Depending on its design, a power supply may obtain energy
from:

Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage.

A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load. Examples of the latter case include the low voltage DC power supplies that are part of desktop computers and consumer electronics devices.
Commonly specified power supply attributes include:

Power supplies types

Power supplies for electronic devices can be broadly divided into
line-frequency (or "conventional") and switching power supplies. The
line-frequency supply is usually a relatively simple design, but it
becomes increasingly bulky and heavy for high-current equipment due to
the need for large mains-frequency transformers and heat-sinked
electronic regulation circuitry. Conventional line-frequency power
supplies are sometimes called "linear," but that is a misnomer because
the conversion from AC voltage to DC is inherently non-linear when the
rectifiers feed into capacitive reservoirs. Linear voltage regulators
produce regulated output voltage by means of an active voltage divider
that consumes energy, thus making efficiency low. A switched-mode supply
of the same rating as a line-frequency supply will be smaller, is
usually more efficient, but will be more complex.

Battery

A battery is a device that converts stored chemical energy to
electrical energy. Batteries are commonly used as energy sources in many
household and industrial applications.
There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries
(rechargeable batteries), which are designed to be recharged and used
multiple times. Batteries come in many sizes, from miniature cells used
in hearing aids and wristwatches to room-size battery banks that serve as backup power supplies in telephone exchanges and computer data centers.

DC power supply

A home-made linear power supply (used here to power amateur radio equipment)

An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors,
to filter out (smooth) most of the pulsation. A small remaining
unwanted alternating voltage component at mains or twice mains power frequency (depending upon whether half- or full-wave rectification is used)—ripple—is unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem,
and the simplest unregulated mains-powered DC power supply circuit
consists of a transformer driving a single diode in series with a resistor.
Before the introduction of solid-state electronics, equipment used valves
(vacuum tubes) which required high voltages; power supplies used
step-up transformers, rectifiers, and filters to generate one or more
direct voltages of some hundreds of volts, and a low alternating voltage
for filaments. Only the most advanced equipment used expensive and
bulky regulated power supplies.

AC power supply

An AC power supply typically takes the voltage from a wall outlet (mains supply) and lowers it to the desired voltage (e.g. 9 VAC), some filtering may take place as well.

Linear regulated power supply

The voltage produced by an unregulated power supply will vary
depending on the load and on variations in the AC supply voltage. For
critical electronics applications a linear regulator
may be used to set the voltage to a precise value, stabilized against
fluctuations in input voltage and load. The regulator also greatly
reduces the ripple and noise in the output direct current. Linear
regulators often provide current limiting, protecting the power supply
and attached circuit from overcurrent.
Adjustable linear power supplies are common laboratory and service
shop test equipment, allowing the output voltage to be adjusted over a
range. For example, a bench power supply used by circuit designers may
be adjustable up to 30 volts and up to 5 amperes output. Some can be
driven by an external signal, for example, for applications requiring a
pulsed output.

]AC/DC supply

In the past, mains electricity was supplied as DC in some regions, AC
in others. Transformers cannot be used for DC, but a simple, cheap
unregulated power supply could run directly from either AC or DC mains
without using a transformer. The power supply consisted of a rectifier
and a filter capacitor.
When operating from DC, the rectifier was essentially a conductor,
having no effect; it was included to allow operation from AC or DC
without modification.

Switched-mode power supply

In a switched-mode power supply
(SMPS), the AC mains input is directly rectified and then filtered to
obtain a DC voltage. The resulting DC voltage is then switched on and
off at a high frequency by electronic switching circuitry, thus
producing an AC current that will pass through a high-frequency transformer or inductor. Switching occurs at a very high frequency (typically 10 kHz — 1 MHz), thereby enabling the use of transformers
and filter capacitors that are much smaller, lighter, and less
expensive than those found in linear power supplies operating at mains
frequency. After the inductor or transformer secondary, the high
frequency AC is rectified and filtered to produce the DC output voltage.
If the SMPS uses an adequately insulated high-frequency transformer,
the output will be electrically isolated from the mains; this feature is often essential for safety.
Switched-mode power supplies are always regulated.[citation needed]
To keep the output voltage constant, the power supply employs a
feedback controller that monitors current drawn by the load. The
switching duty cycle increases as power output requirements increase.
SMPSs often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm.[1]
In the event that an abnormal high-current power draw is detected, the
switched-mode supply can assume this is a direct short and will shut
itself down before damage is done. PC power supplies often provide a power good signal to the motherboard; the absence of this signal prevents operation when abnormal supply voltages are present.
SMPSs have an absolute limit on their minimum current output.[2]
They are only able to output above a certain power level and cannot
function below that point. In a no-load condition the frequency of the
power slicing circuit increases to great speed, causing the isolated
transformer to act as a Tesla coil,
causing damage due to the resulting very high voltage power spikes.
Switched-mode supplies with protection circuits may briefly turn on but
then shut down when no load has been detected. A very small low-power dummy load
such as a ceramic power resistor or 10-watt light bulb can be attached
to the supply to allow it to run with no primary load attached.Power factor has become an issue of concern for computer manufacturers. Switched mode power supplies have traditionally been a source of power line harmonics
and have a very poor power factor. The rectifier input stage distorts
the waveshape of current drawn from the supply; this can produce adverse
effects on other loads. The distorted current causes extra heating in
the wires and distibution equipment. Switched mode power supplies in a
building can result in poor power quality for other utility customers.
Customers may face higher electric bills for a low power factor load.
Some switch-mode power supplies use filters or additional switching
stages in the incoming rectifier circuit to improve the waveform of the
current taken from the AC line. This adds to the circuit complexity.
Many computer power supplies built in the last few years now include
power factor correction built right into the switched-mode supply, and
may advertise the fact that they offer 1.0 power factor.

Programmable power supplies allow for remote control of the output
voltage through an analog input signal or a computer interface such as RS232 or GPIB.
Variable properties include voltage, current, and frequency (for AC
output units). These supplies are composed of a processor,
voltage/current programming circuits, current shunt, and voltage/current
read-back circuits. Additional features can include overcurrent,
overvoltage, and short circuit protection, and temperature compensation.
Programmable power supplies also come in a variety of forms including
modular, board-mounted, wall-mounted, floor-mounted or bench top.
Programmable power supplies can furnish DC, AC, or AC with a DC
offset. The AC output can be either single-phase or three-phase.
Single-phase is generally used for low-voltage, while three-phase is
more common for high-voltage power supplies.
Programmable power supplies are now used in many applications. Some examples include automated equipment testing, crystal growth monitoring, and differential thermal analysis.[3]

An uninterruptible power supply (UPS) takes its power from two or
more sources simultaneously. It is usually powered directly from the AC
mains, while simultaneously charging a storage battery. Should there be a
dropout or failure of the mains, the battery instantly takes over so
that the load never experiences an interruption. Such a scheme can
supply power as long as the battery charge suffices, e.g., in a computer
installation, giving the operator sufficient time to effect an orderly
system shutdown without loss of data. Other UPS schemes may use an
internal combustion engine or turbine to continuously supply power to a
system in parallel with power coming from the AC . The engine-driven
generators would normally be idling, but could come to full power in a
matter of a few seconds in order to keep vital equipment running without
interruption. Such a scheme might be found in hospitals or telephone
central offices.

[]High-voltage power supply

High voltage refers to an output on the order of hundreds or
thousands of volts. High-voltage supplies use a linear setup to produce
an output voltage in this range.
Additional features available on high-voltage supplies can include the ability to reverse the output polarity along with the use of circuit breakers and special connectors intended to minimize arcing
and accidental contact with human hands. Some supplies provide analog
inputs (i.e. 0-10V) that can be used to control the output voltage,
effectively turning them into high-voltage amplifiers albeit with very limited bandwidth.

A voltage multiplier is an electrical circuit that converts AC
electrical power from a lower voltage to a higher DC voltage, typically
by means of a network of capacitors and diodes. The input voltage may be
doubled (voltage doubler), tripled (voltage tripler),
quadrupled (voltage quadrupler), and so on. These circuits allow high
voltages to be obtained using a much lower voltage AC source.
Typically, voltage multipliers are composed of half-wave rectifiers,
capacitors, and diodes. For example, a voltage tripler consists of three
half-wave rectifiers, three capacitors, and three diodes (as in the Cockcroft Walton multiplier).
Full-wave rectifiers may be used in a different configuration to
achieve even higher voltages. Also, both parallel and series
configurations are available. For parallel multipliers, a higher voltage
rating is required at each consecutive multiplication stage, but less
capacitance is required. The voltage rating of the capacitors determines
the maximum output voltage.
Voltage multipliers have many applications. For example, voltage
multipliers can be found in everyday items like televisions and
photocopiers. Other applications can be found in the laboratory, such as
cathode ray tubes, oscilloscopes, and photomultiplier tubes.[4][5]

Power supply applications

Computer power supply

A modern computer power supply is a switch-mode power supply that
converts AC power from the mains supply, to several DC voltages.
Switch-mode supplies replaced linear suplies due to cost, weight, and
size improvement. The diverse collection of output voltages also have
widely varying current draw requirements.

[Welding power supply

Arc welding uses electricity to melt the surfaces of the metals in order to join them together through coalescence. The electricity is provided by a welding power supply, and can either be AC or DC. Arc welding typically requires high currents typically between 100 and 350 amps. Some types of welding can use as few as 10 amps, while some applications of spot welding employ currents as high as 60,000 amps for an extremely short time. Older welding power supplies consisted of transformers or engines driving generators. More recent supplies use semiconductors and microprocessors reducing their size and weight.

A power supply that is built into an AC mains power plug
is known as a "plug pack" or "plug-in adapter", or by slang terms such
as "wall wart". They are even more diverse than their names; often with
either the same kind of DC plug offering different voltage or polarity,
or a different plug offering the same voltage. "Universal" adapters
attempt to replace missing or damaged ones, using multiple plugs and
selectors for different voltages and polarities. Replacement power supplies must match the voltage of, and supply at least as much current as, the original power supply.
The least expensive AC units consist only of a small transformer,
while DC adapters include a few additional diodes. Whether or not a
load is connected to the power adapter, the transformer has a magnetic
field continuously present and normally cannot be completely turned off
unless unplugged.
Because they consume standby power, they are sometimes known as "electricity vampires" and may be plugged into a power strip to allow turning them off. Expensive switched-mode power supplies can cut off leaky electrolyte-capacitors, use powerless MOSFETs,
and reduce their working frequency to get a gulp of energy once in a
while to power, for example, a clock, which would otherwise need a battery.

Overload protection

Power supplies often include some type of overload protection that
protects the power supply from load faults (e.g., short circuits) that
might otherwise cause damage by overheating components or, in the worst
case, electrical fire. Fuses and circuit breakers are two commonly used mechanisms for overload protection.[6]
A fuse contains a short piece of wire which melts if too much current
flows. This effectively disconnects the power supply from its load, and
the equipment stops working until the problem that caused the overload
is identified and the fuse is replaced. Some power supplies use a very
thin wire link
soldered in place as a fuse. Fuses in power supply units may be
replaceable by the end user, but fuses in consumer equipment may require
tools to access and change.
One benefit of using a circuit breaker as opposed to a fuse is that
it can simply be reset instead of having to replace the blown fuse. A
circuit breaker contains an element that heats, bends and triggers a
spring which shuts the circuit down. Once the element cools, and the
problem is identified the breaker can be reset and the power restored.
Some PSUs use a thermal cutout
buried in the transformer rather than a fuse. The advantage is it
allows greater current to be drawn for limited time than the unit can
supply continuously. Some such cutouts are self resetting, some are
single use only.

]Current limiting

Some supplies use current limiting instead of cutting off power if
overloaded. The two types of current limiting used are electronic
limiting and impedance limiting. The former is common on lab bench PSUs,
the latter is common on supplies of less than 3 watts output.
A foldback current limiter reduces the output current to much less than the maximum non-fault current.

Power conversion

The term "power supply" is sometimes restricted to those devices that convert
some other form of energy into electricity (such as solar power and
fuel cells and generators). A more accurate term for devices that
convert one form of electric power into another form (such as
transformers and linear regulators) is power converter. The most common conversion is from AC to DC.